This invention is for a photocoupler comprising a light emitting device and a light detecting device both of which are made of amorphous semiconductors.
The light emitting device may be an amorphous semiconductor thin film light emitting diode whilst the light detecting device may be either 1) an amorphous semiconductor thin film solar cell, or 2) photoconductive-type amorphous semiconductor thin film.
The preferable amorphous semiconductor thin films mentioned here are, for example; amorphous silicon, amorphous silicon carbide, amorphous silicon nitride, amorphous silicon oxide or the combination thereof. Since these amorphous semiconductor thin films can be produced at low cost and on any area, the photocoupler made of these materials can be produced at a lower cost as compared with a conventional crystalline photocoupler, and can be produced at any size. The design and production of the amorphous photocoupler can lead to either a photoisolator type or a photointerrupter type, which will be described in latter sections.
The amorphous semiconductor photocoupler may be operated in either DC mode or pulse mode.
Conventional photocouplers are made of expensive crystalline semiconductors, such as gallium arsenide (GaAs), cadmium sulfide (CdS), indium phosphide (InP), silicon (Si), etc. The fabrication costs for these crystalline materials are quite high, and the fabrications need a large amount of energy, usually in the form of electricity.
Amorphous semiconductor photocouplers may be prepared by low cost glow discharge plasma chemical vapour deposition (CVD) or other vacuum deposition techniques, and can be produced on any area, and at mass production scale.
The photocouplers may use inexpensive substrates such as glass and/or metal sheets.
A description of the architecture of such an amorphous semiconductor thin film light emitting diode has been disclosed in another application by the same applicant AUPM4832 applied for in the United States.
The use of amorphous materials for photocouplers has also been described in U.S. Pat. No. 4,695,859 by Subhendo Guha and Satish Agarwal whereby the combination of a thin film light emitting diode and a photodiode is used to make a new type of copier machine. The principle of that patent is that the light output from the thin film light emitting diode is reflected from a document (paper) and then detected by the photodiode. The light emitting diode and the photodiode are for that reason located sufficiently spatially apart to allow for the detection of scattered light and are thus individual units.
However, one of the features of this invention allows the amorphous thin film solar cell (photodiode) to be fabricated so that it is deposited onto a surface (back surface say) of a common substrate such as glass, whilst the thin film light emitting diode is deposited onto the opposite (front) surface of the common glass substrate. Such an arrangement leads to the reduction of the cost of the photocoupler.
In one form of the invention there is a photocoupler comprising an amorphous semiconductor thin film light emitting diode capable of emitting light in response to an electric stimuli and an amorphous semiconductor photoresponsive light detecting means adapted to detect the light emitted by the thin film light emitting diode.
In a further form of the invention there is proposed a photocoupler including an amorphous semiconductor thin film light emitting diode capable of emitting light in response to an electric stimuli, an amorphous semiconductor photovoltaic light detecting means adapted to detect the emitted light of the thin film light emitting diode, said light emitting diode comprising of a first thin film electrode, a plurality of amorphous semiconductor thin films, an optically transparent second thin film electrode, and an optically transparent substrate, arranged in a sandwich type manner, such an arrangement allowing emission of light through the optically transparent substrate when the light emitting diode is electrically stimulated, said photovoltaic light detecting means comprising of a first thin film electrode, a plurality of amorphous semiconductor thin films, an optically transparent second thin film electrode, and an optically transparent substrate, arranged in a sandwich type manner, the optically transparent substrates of both the light emitting diode and the light detecting means adapted to face each other with a spatial predetermined separation.
In a yet further form a photocoupler including an amorphous semiconductor thin film light emitting diode capable of emitting light in response to an electric stimuli, an amorphous semiconductor photoconductive light detecting means adapted to detect the light emitted by the thin film light emitting diode, said light emitting diode comprising of a first thin film electrode, a plurality of amorphous semiconductor thin films, an optically transparent second thin film electrode and an optically transparent substrate, arranged in a sandwich type manner such an arrangement allowing emission of light through the optically transparent substrate when the light emitting diode is electrically stimulated, and said photoconductive light detecting means comprising of an optically transparent substrate, an amorphous silicon thin film and an ohmic thin film electrode, in a sandwich type arrangement the said photoconductive light detecting means positioned so that its optically transparent substrate faces the optically transparent substrate of the light emitting diode with a spatial predetermined separation.